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标题: 模考时的几道数学题，求救 [打印本页]

作者: eliasfan 时间: 2011-1-26 21:08
标题: 模考时的几道数学题，求救

According to the direction on a can of frozen orange juice concentrate . 1 can of concentrate is to be mixed with 3 cans of water to make orange juice .How many 12-ounce cans of the contentrate are required to prepare 200 6-ounce serving of arange juice?
A 25
B 34
C 50
D 67
E 100

A used-car dealer sold one car at a profit of 25 percent of the dealer’s purchase price for that car and sold another car at a loss of 20 percent of the dealer’s purchase price for that car .If the dealer sold each car for $2,000, what was the dealer’s total profits or loss in dollars for the two transactions combined?

A $1,000 profit

B $2,000 profit

C $1,000 loss

D $2,000 loss

E $3,334 loss

The residents of Town X participated in a survey to determine the number of hours per week each resident spent watching television . The distribution of the results of the survey had a mean of 21 hours and a standard deviation of 6 hours .The number of hours that Pat ,a resident of Town X watched television last week was between 1 and 2 standard deviations below the mean . Which of the following could be the number of hours that Pat watched television last week ?

A 30

B 20

C 18

D 12

E 6

作者: eliasfan 时间: 2011-1-26 21:10
the answer is
A
C
D
but I really want to know the reasoning , who can tell me ?

作者: tanganlang 时间: 2011-1-26 21:31
1. coz the rate of concentrate:Orange=1:4. so 2x:200 =>x=25;
2. $100 loss;
3. the # of P has this inequility: 21-2*6<

<21-6; only 12 btw 7 and 15, so D.

作者: eliasfan 时间: 2011-1-26 22:03
I see ,just now I understood the passage meaning,
thanks all the same

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